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Suggested Citation:"ANALYSIS OF THE STILLBIRTH DATA." National Research Council. 1956. Effect of Exposure to the Atomic Bombs on Pregnancy Termination in Hiroshima and Nagasaki. Washington, DC: The National Academies Press. doi: 10.17226/18776.
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Page 118
Suggested Citation:"ANALYSIS OF THE STILLBIRTH DATA." National Research Council. 1956. Effect of Exposure to the Atomic Bombs on Pregnancy Termination in Hiroshima and Nagasaki. Washington, DC: The National Academies Press. doi: 10.17226/18776.
×
Page 119
Suggested Citation:"ANALYSIS OF THE STILLBIRTH DATA." National Research Council. 1956. Effect of Exposure to the Atomic Bombs on Pregnancy Termination in Hiroshima and Nagasaki. Washington, DC: The National Academies Press. doi: 10.17226/18776.
×
Page 120
Suggested Citation:"ANALYSIS OF THE STILLBIRTH DATA." National Research Council. 1956. Effect of Exposure to the Atomic Bombs on Pregnancy Termination in Hiroshima and Nagasaki. Washington, DC: The National Academies Press. doi: 10.17226/18776.
×
Page 121
Suggested Citation:"ANALYSIS OF THE STILLBIRTH DATA." National Research Council. 1956. Effect of Exposure to the Atomic Bombs on Pregnancy Termination in Hiroshima and Nagasaki. Washington, DC: The National Academies Press. doi: 10.17226/18776.
×
Page 122
Suggested Citation:"ANALYSIS OF THE STILLBIRTH DATA." National Research Council. 1956. Effect of Exposure to the Atomic Bombs on Pregnancy Termination in Hiroshima and Nagasaki. Washington, DC: The National Academies Press. doi: 10.17226/18776.
×
Page 123
Suggested Citation:"ANALYSIS OF THE STILLBIRTH DATA." National Research Council. 1956. Effect of Exposure to the Atomic Bombs on Pregnancy Termination in Hiroshima and Nagasaki. Washington, DC: The National Academies Press. doi: 10.17226/18776.
×
Page 124
Suggested Citation:"ANALYSIS OF THE STILLBIRTH DATA." National Research Council. 1956. Effect of Exposure to the Atomic Bombs on Pregnancy Termination in Hiroshima and Nagasaki. Washington, DC: The National Academies Press. doi: 10.17226/18776.
×
Page 125
Suggested Citation:"ANALYSIS OF THE STILLBIRTH DATA." National Research Council. 1956. Effect of Exposure to the Atomic Bombs on Pregnancy Termination in Hiroshima and Nagasaki. Washington, DC: The National Academies Press. doi: 10.17226/18776.
×
Page 126
Suggested Citation:"ANALYSIS OF THE STILLBIRTH DATA." National Research Council. 1956. Effect of Exposure to the Atomic Bombs on Pregnancy Termination in Hiroshima and Nagasaki. Washington, DC: The National Academies Press. doi: 10.17226/18776.
×
Page 127
Suggested Citation:"ANALYSIS OF THE STILLBIRTH DATA." National Research Council. 1956. Effect of Exposure to the Atomic Bombs on Pregnancy Termination in Hiroshima and Nagasaki. Washington, DC: The National Academies Press. doi: 10.17226/18776.
×
Page 128
Suggested Citation:"ANALYSIS OF THE STILLBIRTH DATA." National Research Council. 1956. Effect of Exposure to the Atomic Bombs on Pregnancy Termination in Hiroshima and Nagasaki. Washington, DC: The National Academies Press. doi: 10.17226/18776.
×
Page 129
Suggested Citation:"ANALYSIS OF THE STILLBIRTH DATA." National Research Council. 1956. Effect of Exposure to the Atomic Bombs on Pregnancy Termination in Hiroshima and Nagasaki. Washington, DC: The National Academies Press. doi: 10.17226/18776.
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Page 130

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Chapter IX ANALYSIS OF THE STILLBIRTH DATA 9.1 The trait. — The definition of a stillbirth employed in this study is an infant who shows no signs of life at birth, following a period of gestation of at least 20 weeks. Any infant that moves, makes respiratory attempts, or is born with a beating heart is not in the strict sense "stillborn." This definition, which is that em- ployed in United States vital statistics, runs counter to current Japanese usage, under which infants who showed signs of life at birth but never succeeded in establishing a pattern of regular respiration are frequently reported as stillborn. This usage was in part a matter of convenience, since a stillbirth required com- pleting only one official form, whereas a live- birth dying an hour following delivery required completing two. The subject of the ABCC's usage of the term "stillbirth" was repeatedly taken up at conferences with the midwives. The frequency of stillbirths encountered in our control material (both parents category 1) was in Hiroshima 1.27 per cent of all births (17,189 births) and in Nagasaki 1.31 per cent (14,450 births). In comparison, in 1950 the "official" stillbirth rate (stillbirths per 1,000 livebirths) was in Hiroshima prefecture 79.6 and in Nagasaki prefecture 87.7, or, expressed as percentage of all births, 7.37 per cent and 8.07 per cent respectively (Public Health and Welfare in Japan, 1950). Official statistics for other years are similar. There is apparent a marked discrepancy between official statistics and our own. There are at least five factors to be taken into account in an evaluation of these differences. Firstly, there is the matter of regis- tration practices referred to above. Secondly, the official stillbirth data are for stillbirths after the third month of uterogestation, whereas by and large our figures refer to events following the fifth month of gestation. Thirdly, since the official figures are for an entire prefecture, there is the possibility of urban-rural differentials. This, however, works in the opposite direction than the first two factors, since in 1950 the stillbirth rate for all shi (cities) was 134.0 per 1,000 livebirths, whereas for all gun (villages and rural areas) the rate was 70.4. Fourthly, the official figures may include some induced termi- nations, whereas these were excluded from our own data. Lastly, those stillborn infants with gross malformations were excluded from our figures. The reasons for this exclusion were given in Section 6.2. When approximate allowance is made for the exclusion from our figures of stillborn, malformed infants, the stillbirth rates observed in this study are quite similar to those currently obtaining in many parts of the United States (e.g., Michigan, 1950, 1.9 per cent). The possi- bility that the ABCC program was failing to obtain data on any substantial number of still- births seems precluded by the efficiency of preg- nancy registration (Sec. 2.1) and the system of careful follow-up for all registered terminations. 9.2 The genetic argument for radiation-in- duced changes. — Animal experimentation on the genetic effects of irradiation indicates that the largest group of induced mutations having clear-cut effects detectable in the first generation of offspring following exposure are the auto- somal lethals. As detected in the first genera- tion of offspring these mutations would consist largely of the dominant lethals, although a few recessive lethals would be recovered due to the fortuitous combination in some individuals of an induced lethal mutant with an allelic lethal mutant of spontaneous origin. Presumably one of the manifestations of the presence of these mutant genes would be fetal death. Accordingly, we might expect, as one of the changes sympto- matic of irradiation-induced genetic damage, an increase in the frequency with which infants are stillborn as parental exposure increases. 9.3 Concomitant variation known to affect 118

Analysis of the Stillbirth Data 119 the stillbirth rate. — No one of the indicators with which we have dealt or shall deal is more complex with respect to concomitant variation than the one presently under consideration. No less than seven sources of concomitant variation known to affect the stillbirth rate could, con- ceivably, be influencing the data which we shall analyze. These seven sources of extraneous vari- ation are congenital syphilis, birth injury, ma- ternal age, parity, nutrition, rate of reproduc- tion, and paternal age. Congenital syphilis has long been one of the major causes of fetal mortality. In Hiroshima and Nagasaki the frequency of positive serolo- gies is from 5 to 7 per cent among post-parturi- ent women. To assess the amount of infantile mortality attributable to congenital syphilis among the births described here would have required an expenditure of time and energy which, because of the limitations of personnel by syphilitic stillborn infants (and we have no evidence that it is not) then, because of the known differential in maternal age among the parental exposure cells, herein lies a possible source of bias. The age distribution among the exposure cells is such that this bias would tend to inflate the stillbirth rate among those parents less heavily exposed or not exposed at all. How- ever, these potential effects would appear to be quite small, of a magnitude which could safely be ignored in this analysis. A second major factor affecting infant sur- vival (which it was not possible to control) is the occurrence of an injury during parturition. In the United States, it has been estimated that birth injury accounts for no less than 13.6 per cent of infantile mortality (Stander, 1941). Of the various types of injuries which may be sustained during the passage of the infant through the birth canal, by far the most common TABLE 9.1 CONGENITAL SYPHILIS AMONG LIVING INFANTS BORN IN NAGASAKI IN 1951 (Incidence and relation to maternal age [after Wright, S.W. et al., 1952]) Maternal age: years Totals Number of living infants.... 6,673 Number of cases of congenital syphilis 47 Incidence X 1,000 7 x'=l 1.160 15-19 181 20-24 1,691 25-29 2,435 30-34 1.456 35-39 735 40-44 171 45-50 4 4 22 17 10 DF=5 16 6.5 5 4 3.4 5.4 P < 0.05 and facilities, was not possible. However, a small study was made in Nagasaki on infants born in the year 1951 in an attempt to deter- mine the incidence of congenital syphilis among the infants being examined in connection with the genetics program (Wright, S. W. et al., 1952). Initially it was planned that this study would estimate the incidence of congenital syphilis among living infants, stillbirths, and neonatal deaths. Because of the formidable diffi- culties posed in estimating the latter incidences in the absence of an exhaustive post-mortem program in Nagasaki, attention had to be fo- cused on living infants alone. Two items of interest here emerged from this study. Firstly, some seven out of every thousand liveborn infants were shown to have congenital syphilis either by clinical, serologic, or roentgenologic examination, or any combination thereof. Sec- ondly, a gradual decline in the rate of trans- mission with increasing maternal age was noted. These latter data are reproduced in Table 9.1. If this same effect of maternal age is exhibited is intra-cranial injury with hemorrhage. It has been reported that 40-80 per cent of infants coming to autopsy will show evidence of this form of birth injury (Stander, 1941). In our own data among 50 autopsied infants, se- lected at random, 26 showed intra-cranial hemorrhages ranging from moderate to severe in degree. While the importance of birth injury in infantile death cannot be gainsaid, it is diffi- cult to visualize circumstances which would lead to a non-random distribution of birth injuries among the parental exposure categories, and this possibility will be ignored in the analysis. A third major factor affecting infant survival is maternal nutrition. The importance of this variable is amply attested to by an extensive literature. In the main, this literature is in agree- ment in indicating that rather drastic changes in maternal nutrition must occur before clearly demonstrable changes in the stillbirth rate can be shown (see, for example, Antonov, 1947, and Smith, 1947). There is no evidence that during the course of this study the limitations

120 Chapter IX Genetic Effects of Atomic Bombs imposed on maternal nutrition by economic conditions prevailing in Japan reached the levels necessary to produce measurable changes in the stillbirth rate, or that (arguing again from the rough classification of economic status presented in Sec. 5.3) such differences in maternal nutri- tion as existed were non-randomly distributed. Among the variables affecting the stillbirth rate previously enumerated, the effects of ma- ternal age and parity are by far the most com- plex and general in scope. These effects as manifested in the present material are sum- marized in Tables 9.2 and 9.3 and Figures 9.1 and 9.2. The data are presented and analyzed in the same manner as age and parity effects with respect to major congenital malformations (cf. Sec. 8.4). Again, a detailed discussion of the findings will be deferred for a subsequent publi- cation. There is a significant effect on stillbirth frequency of both age and parity, with, in both instances, an apparent increase in stillbirth fre- quency at the extremes of the scale. This in- TABLE 9.2 THE EFFECT OF MATERNAL AGE AT FIXED PARITY ON THE FREQUENCY OF STILLBORN INFANTS (The meaning of the symbols employed is explained in Sec. 8.4.) Total Normal Stillborn births births infants Parity 1 < 21 1,912 1,882 30 21-25 8,623 8,479 144 26-30 3,192 3,125 67 31-35 614 595 19 36-40 178-1 41+ 19/ Total 14,538 14,270 268 X=5 = 14.046* IAD = 0.0768 Parity 2 <21 421 415 6 21-25 6,639 6,572 67 26-30 6,354 6,294 60 31-35 1,415 1,399 16 36-40 366 360 6 41+ 47 46 1 Total 15,242 15,086 156 X25 = 3.174 IAD = 0.0387 Parity 3 21-25"!.'"!.! 2.211/ 2'224 23 26-30 5,799 5,729 70 31-35 2,390 2,357 33 36-10 5251 41+ 66/ Total 11,027 10,890 137 X2S = 3.153 IAD = 0.0515 Parity 4 ^-25'!!!!!!!!!!!!!!!!!!!!!!!!! 478J 476 6 26-30 2,848 2,828 20 31-35 2,521 2,487 34 36-40 750 736 14 41 + 84 83 1 Total 6,686 6,610 76 X24 = 9.770* IAD =0.1647 Per cent stillborn 1.57 1.67 2.10 3.09 4.06 pT = 0.2612 1.43 1.01 0.94 1.13 1.64 2.13 pT = 0.2738 1.02 1.21 1.38 1.86 = 0.1981 1.45 0.70 1.35 1.87 1.19 pT = 0.1201 AD .01995 .05687 .03101 .02920 .01661 .15364 .01095 .00615 .03259 .00983 .01460 .00336 .07748 .03634 .01513 .02444 .02703 .10294 .02010 .16468 .07112 .07286 .00060 .32936

Analysis of the Stillbirth Data 121 TABLE 92—Continued Total Normal births births Parity 5 21-25 78 76 26-30 991 975 31-35 1,756 1,737 36-40 837 823 41 + 97 95 Total 3,759 3,706 X24 = 3.116 IAD = 0.1102 Parity 6 21-25 12\ 26-30 262/ 27° 31-35 956 943 36-40 794 785 41+ 141 135 Total 2,165 2,133 X2, = 8.208* IAD = 0.1242 Parity 7 + 21-25 4-1 26-30 57 / 31-35 488 479 36-40 1,195 1,167 41 + 498 483 Total 2,242 2,187 X2a = 3.015 IAD = 0.0799 AH parities <21 2,374 2,337 21-25 18,045 17,801 26-30 19,503 19,265 31-35 10,140 9,997 36-40 4,645 4,556 41+ 952 926 Total 55,659 54,882 X2. = 26.547** Stillborn infants 2 16 19 14 2 53 13 9 6 32 9 28 15 55 37 244 238 143 89 26 Per cent stillborn 2.56 1.61 1.08 1.67 2.06 pT = 0.0675 1.46 1.36 1.13 4.26 = 0.0389 4.92 1.84 2.34 3.01 pT = 0.0403 1.56 1.35 1.22 1.41 1.92 2.73 AD .01723 .03879 .11020 .04208 .01211 .22041 .00158 .03585 .08678 .12421 .24842 .02803 .05538 .02451 .05188 .15980 .00507 .01032 .04472 .00189 .03153 .01659 777 — IAD' (for age) = 0.0761 crease at the lower end of the scale is more definite with respect to parity than with respect to age. One of the more exhaustive previous studies of this relationship of maternal age and parity to infant survival is that of Yerushalmy (1945), who found that (1) "the lowest rates do not occur in one particular age group irrespective of parity. There is a consistent shifting of the minimum rate to the older ages with increasing parity." (2) "When the stillbirth rates by age of mother are compared for the different parity groups the increase in the rate is not propor- tionate for the various age groups. The increase is very much higher for the younger age of mother groups than for the older." The present data appear to agree with the first of these two conclusions, but of themselves would scarcely permit drawing the second conclusion — this may be in part a matter of the numbers involved. From the standpoint of controlling extraneous variation, these findings, taken in conjunction with our own, imply that the only really ade- quate control is one which takes into account not only maternal age but also parity. Among the Japanese data, to effect an adequate control would require recognizing approximately 25 parity-specific age intervals (five intervals for parity, and five for age, or 25 in all). The data, because of the already existing numerous ways

122 Chapter IX Genetic Effects of Atomic Bombs TABLE 9.3 THE EFFECT OF MATERNAL PARITY AT FIXED AGE ON THE FREQUENCY OF STILLBORN INFANTS (The meaning of the symbols employed is explained in Sec. 8.4.) Total births Normal births Mother's age: < 21 1 1.912 1,882 2 421 415 3+ 41 40 Total 2,374 2,337 X2, = 0.257 IID = 0.0154 Mother's age: 21-25 1 8,623 8,479 2 6,639 6,572 3 2,211 2,188 4 478 472 5 78\ 6+ 16J Total 18,045 17,801 X24 = 19.969** I*D = 0.1252 Mother's age: 26-30 1 3,192 3,125 2 6,354 6,294 3 5,799 5,729 4 2,848 2,828 5 991 975 6 262 259 7+ 57 55 Total 19,503 19,265 X\ = 34.577** IAD = 0.1415 Mother's age: 31-35 1 614 595 2 1,415 1,399 3 2,390 2,357 4 2,521 2,487 5 1,756 1,737 6 956 943 7+ 488 479 Total 10,140 9,997 X2e = 15.444* KD = 0.0884 Mother's age: 36-40 1 178 171 2 366 360 3 525 514 4 750 736 5 837 823 6 794 785 7+ 1,195 1,167 Total 4,645 4,556 X2 = 8.111 UD = 0.1104 Stillborn infants 30 6 1 37 144 67 23 6 244 67 60 70 20 16 3 2 238 19 16 33 34 19 13 9 143 7 6 11 14 14 9 28 89 Per cent stillborn 1.57 1.43 2.44 = 0.0427 1.67 1.01 1.04 1.26 4.26 = 0.3242 2.10 .94 1.21 .70 1.61 1.15 3.51 pT = 0.3504 3.09 1.13 1.38 1.35 1.08 1.36 1.84 pT = 0.1822 3.93 1.64 2.10 1.87 1.67 1.13 2.34 pT = 0.0835 AD .00551 .01542 .00991 .03084 .11384 .09460 .02865 .00193 .01133 .25035 .11930 .07461 .00326 .06276 .01662 .00083 .00555 .28293 .07335 .02805 .00500 .01101 .04088 .00342 .01503 .17674 .22082

Analysis of the Stillbirth Data 123 Mother's age: 41 + 1 2 3 4 5 6 7+ Total X*4 = 3.030 TABLE 9.3—Continued Total births 19 47 66 84 97 141 498 3 .. 4 .. 5 .. 6 .. 7 + Normal Stillborn Per cent births infants stillborn 18 1 5.26] 46 1 2.13 66 — -J 83 1 1.19 95 2 2.06 135 6 4.26 483 15 3.01 952 926 IAD = 0.1403 All ages 1 14,538 2 15,242 11,027 6,686 3,759 2,165 2,242 Total 55,659 X\ = 59.978** 14,270 15,086 10,890 6,610 3,706 2,133 2,187 54,882 26 268 156 157 76 53 32 55 pT = 0.0171 1.84 1.02 1.24 1.14 1.41 1.48 2.45 777 — IAD" (for parity)= 0.1186 AD .06346 .05117 .02567 .08499 .05533 .28062 .08491 .07411 .02211 .02263 .00068 .00231 .03094 5-0 4.5 4.0- 3.5 3.0 2.5 STILLBIRTHS (PER CENT) 2.0 1.5 1.0 • 0.5 15 20 25 30 MOTHER'S AGE 40 45 FIGURE 9.1 — The distribution of the frequency of stillborn infants by age of mother for specified parities.

124 Chapter IX Genetic Ejects of Atomic Bombs 4.5T 4.0 3.5- 3.0- 2.5 STILLBIRTHS (PER CENT) 2.0 1.5 1.C 0.5 6 H 7* 12345 PARITY FIGURE 92 — The distribution of the frequency of stillborn infants by parity for specified maternal ages. of classification, would not permit so elegant an approach to the extraneous variation occasioned by mother's age and parity. Accordingly, it became a matter of judgment as to which of these two factors was to be controlled. A de- cision was reached to disregard age but to recognize, for analytical purposes, five parity classes, namely, parity 1, parities 2-3, 4-5, 6-7, and 8 and higher. 9.4 The data. — Tables 9.4 and 9.5 present the distribution and analysis of stillborn infants by sex, city, and parental exposure without fur- ther subdivision by parity. Inspection of Table 9.4 suggests a difference in the stillbirth rate when the mother was not exposed as opposed to when she was. From the analytical table (9.5a) we note a significant effect of mother's exposure but not of sex or father's exposure. Attention is called to the fact that the sex- mother's exposure interaction is not significant, in contrast to expectation in view of the possi- ble effect of exposure on the sex ratio described in Chapter VII. With regard to the reality of the effect of mother's exposure on the stillbirth rate, it should be borne in mind that these data are uncorrected for parity and the more heavily exposed cells are biased in a way which would increase the stillbirth rate in these cells. If in the analysis of Table 9.4 we limit our attention to those exposure cells in which both parents were exposed, which would reduce the differ- ences between cells with regard to parity, the apparent effect of maternal exposure disappears (see Table 9.5b). This observation is of con- siderable importance in the interpretation of these data since (a) maternal exposure con- founds the effects of genetic and somatic damage and hence a significant effect of maternal expo- sure not reflected in paternal exposure might well be a somatic rather than a genetic effect, and (b) there is evidence which has been pre- sented in Chapter V and elsewhere in this report that the comparison of pregnancy ter- minations occurring to exposure category 1 par- ents with terminations occurring to parents in any other exposure category is biased. Let us now turn to a consideration of what these data reveal when the sex of the infant is ignored but terminations are classified with re- spect to parity. Tables 9.6 and 9.7 present the

Analysis of the Stillbirth Data 125 TABLE 9.4 FREQUENCY OF STILLBIRTHS BY SEX, PARENTAL EXPOSURE AND QTY (Unrelated parents) Male infants Hiroshima Fathers 1 2 3 4-5 Total • 'f 8,919 114 .0128 761 309 5 .0162 208 10,197 131 .0128 IP 10 .0131 2 .0096 f" 2,796 924 195 121 4,036 21s 36 15 5 5 61 IP .0129 .0162 .0256 .0413 .0151 B fn 1,108 220 266 80 1,674 -5 • 'l s [p .0244 27 .0045 1 .0301 8 1 37 g .0125 .0221 fn 565 108 52 56 781 4-5-U IP 14 — 1 — 15 .0248 — .0192 — .0192 fn 13,388 2,013 822 465 16,688 TotaK s 191 26 19 8 244 IP .0143 .0129 .0231 .0172 .0146 Male infants Nagasaki Fathers 1 2 3 4-5 Total fn 7,527 1,108 125 73 8,833 M s 110 21 1 1 133 IP .0146 .0190 .0080 .0137 .0151 f 4,809 2,087 140 103 7,139 21s " 77 32 3 — 112 IP .0160 .0153 .0214 — .0157 fn 355 132 50 13 550 31s IP 6 1 — — 7 3 .0169 .0076 — — .0127 fn 276 56 18 15 365 4-5 s 2 1 — — 3 IP .0072 .0179 — — .0082 fn 12,967 3,383 333 204 16,887 TotaK s U 195 .0163 55 4 1 255 .0150 .0120 .0049 .0151

126 Chapter IX Genetic Effects of Atomic Bombs TABLE 9.4—Continued Female infants Hiroshima Fathers 1 2 3 4-5 Total " 8,190 720 280 183 9,373 xr IP 104 9 9 6 128 .0127 .0125 .0321 .0328 .0137 fn 2,512 897 186 121 3,716 2r IP 46 11 4 3 64 .0183 .0123 .0215 .0248 .0172 [" 1,060 202 248 76 1,586 1 , 3V IP 21 3 2 1 27 .0198 .0149 .0081 .0132 .0170 fn 539 91 55 60 745 4-5^ s IP 6 1 — 2 9 .0111 .0110 — .0333 .0121 fn 12,301 1,910 769 440 15,420 Total \ s 177 24 15 12 228 IP .0144 .0126 .0195 .0273 .0148 Female infants Nagasaki Fathers 1 2 3 4-5 Total fn 6,923 1,040 112 64 8,139 Js IP .0116 80 .0163 17 — — .0119 97 — — f" 4,430 2,016 133 73 6,652 21$ 57 49 2 3 111 IP .0129 .0243 .0150 .0411 .0167 8 fn 382 142 43 21 588 |. 3 s 9 3 12 1 IP — .0236 .0211 — — .0204 fn 276 60 17 13 366 4-5-U IP .0145 4 .0333 2 .0588 1 — .0191 7 — fn 12,011 3,258 305 171 15,745 Total { s 150 71 3 3 227 IP .0125 .0218 .0098 .0175 .0144

Analysis of the Stillbirth Data 127 TABLE 9.5 CHI-SQUARE ANALYSIS OF THE FRE- QUENCY OF STILLBIRTHS BY SEX, PARENTAL EXPOSURE, AND CITY (Unrelated parents) a. AH exposure cells (4 X 4) Source Total Interactions, first order CM CF CS SM SF MF DF x' P 63 92.343 .01-.02 3 .620 .80-.90 3 10.626 .01-.02 1 0.200 .50-.70 3 1.565 .50-.70 3 5.499 .10-.20 9 5.548 .70-.80 Main effects Cities (C)' Mother's exposure — 1... Mother's exposure — 2... Mother's exposure — 3... Mother's exposure — 4,5. 1 0.069 .70-.80 1 0.001 .95-.9S 1 0.393 .50-.70 1 0.140 .70-.80 Sum 4 0.603 .95-.9S Sex (S)* Mother's exposure — 1... Mother's exposure — 2.. 1 0.725 .30-.50 1 0.661 .30-.50 Mother's exposure — 3... 1 0.202 .50-.70 Mother's exposure — 4, 5. 1 0.065 .70-.80 Fathers (F)' Mother's exposure — 1 . . . 3 3.943 .20-.30 Mother's exposure — 2 . . . 3 6.769 .05-.10 Mother's exposure — 3 . .. 3 4.192 .20-.30 Mother's exposure — 4, 5. 3 0.187 .95-.9S Sum . . 12 15.091 .20-.30 b. Excluding parents in category 1 (3 X3) Total . . 35 14.186 .50-70 Interactions, first order CM . 2 2 001 30- 50 CF 2 4 121 10-20 CS 1 5 737 01 02 SM 2 2 083 30- 50 SF 2 4 825 05 10 MF 4 0.781 .90-.95 Main effects Sex (S) 1 1.884 .10-.20 Cities (C) 1 1.150 .20-.30 Mothers (M) 2 2.816 .20-.30 Fathers (F) 2 0.388 .80-.90 * Adjusted for mothers.

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Analysis of the Stillbirth Data 129 distribution and analysis of stillborn infants by city and parental exposure with further sub- division by parity. It should be noted that, as expected, there are significant differences in the stillbirth rate among different parities. From Table 9.7 we further note that when all ex- posure cells are considered with reference to TABLE 9.7 CHI-SQUARE ANALYSIS OF THE FREQUENCY OF STILLBIRTHS BY PARENTAL EXPOSURE, CITY, AND PARITY (Unrelated parents) stillbirth frequencies with increasing paternal exposure. To the end of determining whether this apparent effect was explicable in terms of the residual variation in maternal age not re- moved by the parity classification, Table 9.9 was prepared. An examination of this table reveals a number of points of interest. Of the five age groups investigated, the stillbirth rate increases with paternal exposure in three and decreases in two. In one of the three age groups (21-25) the increase with paternal exposure primarily Source Total DF x' p TABLE 9.8 THE FREQUENCY OF STILLBIRTHS AMONG .OOl-.Ol FIRSTBORN INFANTS BY CITY AND PATERNAL EXPOSURE (Unrelated parents) .80-.90 ' Interactions, first order CM . 159 221.950 3 0.620 10.626 8.925 5.548 9.060 16.085 CF 3 .01-.02 City A MF 9 .70-.80 .50-.70 .10-.20 fn Hiroshima Nagasaki 8,162 5,937 159 89 .0195 .0150 Total 14,099 248 .0176 PM . . 12 PF . . 12 is Main effects Parity (P) IP I" City (C)' 4 53.599 8.965 <.001 .10-.20 T 18 34 .0224 .0302 803 1,125 1,928 52 Mothers (M)' Parity Class Class Class Class Class 5 IP .0270 1 3 4.879 7.537 4.008 4.269 2.003 .10-.20 a .05-.10 Jt. .20-.30 £ .20-.30 .50-.70 fn 344 113 13 2 .0378 .0177 457 15 .0328 2 3 3 s [P 3. . . . 3 4 3 f" 4-5 \s 213 52 11 1 .0516 .0192 265 5 3 IP 12 .0453 All classes 15 22.696 .05-.10 Fathers (F)' Parity Class Class Class Class Class fn 9,522 Total-; s 201 IP -0211 7,227 16,749 126 327 .0174 .0195 1. . . . 3 21.749 1.865 0.518 3-521 1.117 < .001 .50-.70 -90-.95 .30-.50 fef •70-80 sta 2 3 3 3 4 3 ects a "1" vs. "non-1" nee, then, when maternal difference. In sub- age as well as parity emerges no clearly 5 3 All classes 15 28.770 .01-.02 is taken into account, there * Adjusted for parity. parity, there is no effect of city or of maternal exposure. However, an effect of paternal ex- posure significant at the 5 per cent level now appears. Inexplicably this latter effect seems to be largely, if not entirely, attributable to those fathers whose infants were firstborn. The fre- quency of stillbirths among firstborn infants by city and paternal exposure is presented in Table 9.8. The data suggest a regular increase in consistent relationship between paternal ex- posure and the stillbirth rate. 9.5 Summary. — Analysis of the stillbirth data, taking into account differences between exposure cells in the parity distributions, fails to reveal significant differences between cities or consistent significant effects of parental ex- posure. The deviations from expectation ob- served are so small and inconsistent that they can scarcely be labeled as favoring or not favor- ing genetic hypothesis.

130 Chapter IX Genetic Effects of Atomic Bombs TABLE 9.9 THE FREQUENCY OF STILLBIRTHS AMONG FIRSTBORN INFANTS BY PATERNAL EXPOSURE AND MATERNAL AGE (Unrelated parents) Fathers Maternal " age 1 2 3 4-5 Total <2o{" 1,772 356 78 29 2,235] 38 I TP .0164 29 .0225 8 .0128 1 — .0170J — 21 f" 8,505 1,031 247 141 9,924] ' "jp 138 26 7 3 1741- .0162 .0252 .0283 .0213 .0175J f" 3,100 372 84 » 3,612] 26-30^ s IP 63 8 5 4 .022lJ 80 I .0203 .0215 .0595 .0714 fn 564 109 29 26 728] 31-35JS 13 7 — 1 21 I .0230 .0642 — .0385 .0288J fn 144 51 16 11 222] 4 3 1 4 12 L IP .0278 .0588 .0625 .3636 .054 ij 41+Js f 14 9 3 2 28] IP .0714 1 — .3333 1 — .0714] 4 — — fn 14,099 1,928 457 265 16,749") TotaU s IP .0176 248 52 15 12 .0195] 327}- t Classes 3 and 4-5 are pooled. .0270 .0328 .0453 V2 X 2 1.055 5.908 11.962** 5.768 11.047**

Next: THE ANALYSIS OF THE BIRTHWEIGHT DATA »
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